The present invention generally relates to color video signal recording systems and color video signal recording and reproducing systems, and more particularly to a system for recording and reproducing a color video signal so that a high-quality reproduced picture can be obtained upon reproduction, even in a system which records the color video signal in a manner such that recorded positions of horizontal synchronizing signals in the color video signal are not aligned in mutually adjacent tracks which are formed on a recording medium in contiguous contact without a guard band between the mutually adjacent tracks.
Generally, in the recording system of a SECAM system color video signal recording and/or reproducing system, for example, a SECAM system color video signal is supplied to a lowpass filter and a bandpass filter, and a luminance signal is separated and filtered in the lowpass filter while a carrier chrominance signal is separated and filtered in the bandpass filter. As is well known, the above carrier chrominance signal is a signal in which a first frequency modulated signal which is obtained by frequency-modulating a first chrominance subcarrier by a color difference signal B-Y, and a second frequency modulated signal which is obtained by frequency-modulating a second chrominance subcarrier by a color difference signal R-Y, are time-sequentially multiplexed in an alternate manner for every one horizontal scanning period (lH). The above carrier chrominance signal having a carrier frequency of 3.9 MHz to 4.75 MHz, for example, is supplied to a frequency dividing circuit wherein the carrier chrominance signal is frequency-divided and converted into a low frequency range. Moreover, the carrier frequency of the carrier chrominance signal is set to a frequency in a range of 0.97 MHz to 1.19 MHz, for example, and the frequency deviation width is reduced. The carrier chrominance signal which is frequency-converted into the low frequency range and the frequency modulated luminance signal, are subjected to a frequency-division-multiplexing and then amplified to be formed into a composite color video signal. This composite color video signal is supplied to a pair of rotary heads having gaps of mutually different azimuth angles.
On the other hand, in the reproducing system, the pair of rotary heads alternately reproduce the composite color video signal which is recorded on the magnetic recording medium (magnetic tape). The outputs of the pair of rotary heads are respectively amplified, and are formed into a continuous signal by being switched alternately in a switching circuit. The frequency modulated luminance signal in this continuous signal, is separated and filtered in a highpass filter, and is then demodulated and converted into the luminance signal in a demodulating circuit. The frequency converted carrier chrominance signal in the continuous signal, is separated and filtered in a lowpass filter, and is then supplied to a multiplying circuit wherein the carrier frequency is restored into the original carrier frequency. The output of this multiplying circuit is supplied to a bandpass filter so as to obtain a predetermined frequency band. The reproduced carrier chrominance signal and the reproduced luminance signal from the demodulating circuit, are multiplexed and formed into a reproduced SECAM system color video signal in a multiplexing circuit.
As one example of a track pattern formed on the magnetic tape according to the above described recording and/or reproducing system, there is a track pattern in which mutually adjacent tracks are formed on the magnetic tape without a guard band formed between the adjacent tracks, by use of a pair of rotary heads having gaps of mutually different azimuth angles. According to this type of a track pattern, crosstalk components from the adjacent tracks are included within the reproduced signal when one rotary head scans over one track. Upon reproduction, there is essentially no crosstalk component related to the luminance signal which is frequency-modulated upon recording, because the azimuth loss is large with respect to the high-frequency luminance signal. On the other hand, the crosstalk component related to the carrier chrominance signal which is frequency-converted into the low frequency range upon recording, is reproduced because the azimuth loss is relatively small with respect to the low-frequency chrominance signal.
Generally, the recording is carried out so that the positions where the horizontal synchronizing signals are recorded, are aligned in a direction perpendicular to the longitudinal direction of the track (so-called H-alignment). Moreover, the recording is carried out so that substantially the same modulated signal components in the frequency converted carrier chrominance signal are adjacent to each other. As a result, the frequency of the frequency converted carrier chrominance signal which is reproduced from one track and the frequency converted carrier chrominance signals which are reproduced from tracks which are adjacent to this one track become substantially the same, because there is correlation among the color video signal components in every one field interval, and because the recording is carried out so that substantially the same modulated signal components are adjacent to each other. Therefore, the frequency difference between the frequency converted carrier chrominance signal which is reproduced from the one track and the frequency converted carrier chrominance signal which is reproduced from the track which is adjacent to the one track is substantially zero, and no beat is introduced. Accordingly, there is virtually no effect of crosstalk among the mutually adjacent tracks with respect to the frequency converted carrier chrominance signal.
It is sometimes desirable to carry out recording and/or reproduction of a long duration. When carrying out such a long-duration recording and/or reproduction in a magnetic recording and/or reproducing apparatus which forms the track pattern described heretofore, only the tape traveling speed is reduced. That is, the diameter of the drum which carries the rotary heads, the tape width, the rotational speed of the drum, and the number of horizontal scanning lines all remain unchanged. When carrying out four hours of recording and/or reproduction by use of a magnetic tape which is designed for two hours of recording and/or reproduction, for example, only the tape traveling speed is reduced to 1/2 the tape traveling speed which would otherwise be used for two hours of recording and/or reproduction with such a magnetic tape. In the track pattern obtained when four hours of recording and/or reproduction is carried out by use of the magnetic tape which is designed for two hours of recording and/or reproduction, the positions where the horizontal synchronizing signals are recorded are not in alignment in the mutually adjacent tracks (that is, not in H-alignment). Accordingly, no correlation exists between the adjacent tracks, and the carrier frequencies of the carrier chrominance signal in the low frequency range differ in the adjacent tracks. In this case, because the adjacent tracks are recorded by the rotary heads having gaps of mutually different azimuth angles, the azimuth loss of the frequency modulated luminance signal becomes large in the high frequency range. As a result, with respect to the frequency modulated luminance signal, there is little effect of crosstalk from the adjacent tracks. However, the azimuth loss of the recorded carrier chrominance signal is small because the recorded carrier chrominance signal is in the low frequency range. The effect of crosstalk from the adjacent tracks is large with respect to the carrier chrominance signal, since the carrier frequencies of the recorded carrier chrominance signal differ in the adjacent tracks. Thus, beat interference is introduced.
On the other hand, if a guard band is formed between the adjacent tracks so as to eliminate the crosstalk, the track width of the heads must be reduced in order to provide the same recording and reproducing time as a recording and reproducing apparatus employing the azimuth recording and reproducing system, with respect to the same length of magnetic tape. However, if the track width of the heads is reduced, the signal-to-noise (S/N) ratio of the reproduced signal becomes deteriorated compared to the S/N ratio of the reproduced signal obtained in a recording and reproducing apparatus which does not form such a guard band between the adjacent tracks. On the other hand, if an attempt is made to maintain the same S/N ratio as the S/N ratio obtained in the recording and reproducing apparatus which does not form the guard band, the recording density on the magnetic tape becomes low and the recording and reproducing time becomes shortened. In addition, if the guard band is formed between the adjacent tracks, there is a problem in that noise bar is generated in the reproduced picture during special reproduction modes of the recording and reproducing apparatus.
Further, an NTSC system color video signal may be recorded and reproduced without forming a guard band between the adjacent tracks, as disclosed in a U.S. Pat. No. 4,178,606 of which the assignee is the same as the assignee of the present application. However, as disclosed in this U.S. patent, measures must be taken to eliminate the effects of crosstalk (as in the case of the recording and reproduction of a PAL system color video signal). Such measures include recording the carrier chrominance signal which is frequency-converted in the low frequency range onto one of the adjacent tracks so that the phase of the frequency converted carrier chrominance signal is shifted in a specific direction by 90.degree. for every one horizontal scanning period, and recording the frequency converted carrier chrominance signal onto the other of the adjacent tracks so that the phase of the frequency converted carrier chrominance signal is shifted in a direction opposite to the above specific direction by 90.degree. for every one horizontal scanning period. Accordingly, when recording and reproducing the NTSC system color video signal, it was necessary to provide phase shifting means for performing the above phase shift, in both the recording system and the reproducing system. Therefore, there were disadvantages in that the circuit construction became complex and the cost of the system as a whole became high.